The present invention is directed to an improved roadway marker base structure, and specifically, to the type of marker base having a downwardly-facing, generally waffle-shaped structure, with downwardly-facing open chambers, which is fixed to a pavement surface by adhesive means.
Historically, many types of roadway markers were used, such as a daytime ceramic marker employed by the State of California in the early 1960's. This particular marker consisted of a solid piece of ceramic material with a high gloss, domed top and bumped protrusions on the bottom. The bottom configuration could not deviate more than 0.05 inches from a flat surface. These bumped protrusions enhanced the bottom surface area of the marker for cooperation with an associated adhesive material when the marker base was affixed to a roadway surface. However, a nighttime marker requires reflective portions which may be more easily added to the top of a marker base made from plastic.
From a manufacturing perspective, not only would it be prohibitively expensive to make a solid plastic marker base to the thickness of the prior art ceramic model, but also such a marker would suffer from shrinkage during the molding process. Thus, any design for a plastic marker base must maintain reasonably small wall thicknesses. Hence, the prior art evolved to use of a thermoplastic shell molded with plastic ribs in a waffle-like arrangement as found in U.S. Pat. No. D-267,933 issued Feb. 15, 1983. The design of such a marker includes chamber walls which are downwardly tapered to a narrow dimension at the roadway surface to provide a draft for ready removal of the marker from the mold. At the same time, the small bottom surface area of these chamber walls does not permit inclusion of large bumped protrusions during the molding process. Therefore, the downward facing surfaces of the chamber walls are coplanar and rest on the roadway surface. These markers are installed by depositing a suitable adhesive, such as bitumin or epoxy, on either the roadway surface or the underside of the marker base so that the adhesive is sandwiched between the roadway surface and the marker base. Downward pressure is then applied to seat the marker base in the adhesive.
If, in the installation as above-described, the marker is fully seated on the pavement with sufficient downward pressure, it has been found that substantially all of the adhesive is squeezed upward into the chambers of the base, thus leaving only a thin film of adhesive between the thin, downwardly facing support surfaces and the roadway surface. This "cookie cutter" effect provides very little adhesive between the road surface and the opposing marker base surfaces to anchor the marker base to the pavement. This sometimes has resulted in markers of this character being too easily knocked off of or accidentally removed from the road.
Another disadvantage of the prior art roadway marker stems from the choice of adhesive material. Epoxy has been commonly used, and it works very well on concrete surfaces; however, it takes a considerable amount of time (15-20 minutes) to set up, thereby necessitating closing off sections of the roadway with cones for extended periods of time. This is particularly inconvenient for temporary marker applications where quick installation is desirable. Moreover, both temporary and permanent markers are frequently used on asphalt surfaces. But, when epoxy is used on asphalt roadways, there may be long-term effects with a crack forming around the epoxy in the asphalt, generally referred to as "reflective cracking." Under those conditions, a marker, the epoxy, and part of the asphalt itself ultimately may be knocked out.
It has been found that bituminous adhesives are more suitable for placement on asphalt, concrete, and chipped-seal-type road surfaces. They are asphaltic materials with a homogenously mixed mineral filler as is well known to those skilled in the art. They eliminate the reflective cracking which appears when epoxy is used on the asphaltic surface. In addition, bitumin sets up normally in 30 seconds to a minute, and, therefore, the labor required for installation of markers with adhesives of that character is significantly reduced.
Bituminous adhesive also is more often used with "temporary" marker installations, such as in construction zones, where epoxy cannot be used because one would not be easily able to remove the epoxy-installed markers from the roadway without tearing up the roadway, whereas the bituminous adhesive can be scraped off. Therefore bituminous adhesively affixed markers are suitable for both permanent and temporary installations. However, because the bituminous material is somewhat flexible (which gives it the ability to be removed from the road), difficulties have arisen with respect to mounting open-shell-type markers of the prior art, such as that found in U.S. Pat. No. D-267,933. Because of such flexibility, the adhesive connection between the shell and the bottom suffers from the problem previously described.
The present invention overcomes the adhesion problem by providing anchoring surfaces on the bottom walls of the marker, which facilitate both a mechanical and adhesive interlock when the marker is installed. The bituminous material is allowed to flow into the chambers, and the marker can be easily installed by simply stepping down on it after the bitumen is applied to the roadway surface in a heated, relatively free-flowing state. The bituminous material can then flow in and around the anchoring surfaces and provide very strong and tough bonding, both for temporary and permanent marker installation.